Electrostatic precipitator

ABSTRACT

An electrostatic precipitator in which the gas flow passage converges in height and diverges in width from inlet to outlet, but is of constant cross-sectional area throughout its entire length. The aspect ratio is constant for one direction of gas flow. The precipitator is divided by discharge electrodes into a number of gas flow sub-passages. Each sub-passage is of constant cross-sectional area and constant aspect ratio.

United States Patent 1191 Grisell July 1, 1975 [54] ELECTROSTATIC PRECIPITATOR 1.445.662 2/1923 Bredley /154 X 1 wanton Chm GM. w 5113113528 21132? $333115::::::::::::::::::::;ff!'$2811; 73 Assign; Rust E l h compmy' 3.425.189 2/1969 Haselmayer 98/40 R X Birmingham. Ala.

' 1 Filed: y 1974 Primary Examiner-Dennis E. Talbert. Jr.

[21] App]. No.: 475.124

1521 u.s. c1. 55 129; 55/110; 55/112; 571 5 ABSTRACT 55/130; 55/136; 55/151; 55/154; 133/37 [51 1 1M. CL; 303C 3/36 1 An clgctrosmfic prgcipitator in which the gas fl Fkld Search 7 sage converges in height andvdiverges in width from 55/133. 13 8. 1 inlet to outlet. but is of constant cross-sectional area 1 11 /3 103. 111. throughout its entire length. The aspect ratio is con- 1 117. 178'. 98/ 3. 19. 3 37. 0 stant for one direction of gas flow. The precipitaior is 40 40 42 divided by discharge electrodes into a number of gas 1 flow sub-passages. Each sub-passage is of constant [56] References Cited cross-sectional area and constant aspect ratio.

UNITED STATES PATENTS 1.442.052 1/1923 Dane... 55/129 10 Claims. 5 Drawing Figures SHEET AIR FLOW 1 v ELECTROSTATIC PRECIPITATOR BACKGROUND OFTHEVINVENTION cipitators and more are charged by passing near a charged discharge electrode. and then are exposed to a similarly charged col- FihallyJthere are the practical considerations of manufacturing cost. spacefor installation. and power required foroperation.

it :can readily be;seen that the above factors are largely interrelated with'one another. so that a change in one affects all. This has causeddifficulty in designing versatile precipitators. and the prior art designs quite often sacrificed certain of the factors in favor of others.

lection electrode. to which they are attracted and adhere. thus removing them from the gas stream. At periodic intervals the particles are removed from the collection electrodes by mechanical or electrical means.

A number of factors govern the efficiency of ttn electrostatic precipitator. Chief among them are: aspect ratio. gas velocity. migration velocity. retention time. and resistivity.

The aspect ratio of the gas passage is the distance from thepoint of measurement to the outlet (length) divided by the height at the point of measurement. The aspect ratio reflects the probability of removing the particles. The greater the aspect ratio at a particular point. the better the chances of the particles being coliected between that point and the outlet. This would suggest that the best design is a very long. low precipitator. but practical considerations limit the length and configuration in most cases. Prior art precipitators have generally been of constant height. and therefore have a diminshing aspect ratio. which means that the farther a particle proceeds into the precipitator. the greater its chances of not being collected.

The velocity of the gas moving through the precipita- ,lor is. of course. quite important. An abnormally high velocity willdecreasc the number of particles that are collected because they will move too swiftly to be propcrly charged and collected. High gas velocity will increase the chances of 're-entraining particles that have once adhered to the collection electrodes. Too low it velocity will mean that comparatively little gas-can be treated in a given time. although the efficiency of the prccipitator may be high.

An additional velocity component is imparted to the 7 gas stream by the action of the charged particles moving toward the collection electrodes. Called the-particle migration velocity. this is a function of a number of factors. including the strength of the electrostatic field. the

number and spacingof the collection electrodes. the resistivity of the individual particles. and the composition of the gas. A charged particle must possess in migration velocity sufficiently high as to insure that it reaches a collection electrode.

The particle retention time is also a function of a number of factors. principally the length of the precipitator and the gas velocity. The longer a particle is retained in the precipitator. the better the chances of coliccting it. Again. practical considerations govern this 7 factor. A long particle. retention time will tend to counterbalance an undesirable aspect ratio.

Also. there are the electrostatic characteristics of the system. known as the resistivityv of the particles. The

- chief consideration here is the ability of the individual particles to accept an electrostatic charge. Governing factors are the ntagnitttdeofthc charges applied to the electrodes and the clcctrostatic characteristics of the particles. Generally. the greater the charge applted to tilt particles. the greater the chances of collection.

, tors cannot accommodate changes in one of the governing factors. such as gas velocity. and in the face of such they lose their efficiency.

SUMMARY OF THE INVENTION The primary object of this invention isto provide an electrostatic precipitator that eliminates the deficiencies found in prior art devices.

A further object of this invention is to provide an electrostatic precipitator that is more efl'tcient than prior art devices.

Another object of this invention is to provide an electrostatic precipitator that is more versatile than the prior art devices. 7 7

in this invention. the aspectratio is kept constant throughout the length of the precipitator. This means that the height of the preclpitator lessens from inlet to outlet. Thus. the chances of a particle being'captured remain constant. and the efficiency of the precipitator is greatly enhanced.

it has also been found to be advantageous to combine with the above feature a constant cross-sectional area.

Thereby. the gas velocity will remain constant from inlet to outlet and the design of the flow characteristics. electrical power requirements. and the like are greatly simplified. By this design. it has been found that the basic efficiency is maximized. Thereafter. the other factors named above can be considered much more objectively.

BRIEF oesctttrrtotv or THE DRAWINGS FIG. 4 is a graph of the aspect ratios forthe prior art device of FIG. 3 and the inventive deviee'of FIGS. l A.

DESCRIPTION OF A PREFERRED EMBODIMENT A preeipitator constructed in accordance with the V teachings of this invention is shown in FiGS. IA. lB

and 2. it comprisesa pair-oi sides 12 and 14. a bottom i would otherwise be the apex of the triangle. extending between station 4 and 5.

There is unimportant relationship between the slope of the hypotenuse 28 of each of sides 12 and i4 and the base 32 of the triangle. as shown in FIG. lB. As explained-abovc. the aspect ratio is the'ratio. at any given point along the length of the gas flow passage. of the of the three sub-passages 5 2. 54 and 56 remains the same for the entire length of each. as does the crosssectional area of each. Subpassages 52. 54 and 56 widen toward outlet 22. and it may be advantageous to further divide them by additional collection plates 60. 62 and 64. which extend over only a portion of the length of each passage 52. 54 and 56. These additional t sub-passages 66. 68. 70. 72. 74 and 76 also have constant aspect ratios and constant cross-sectional areas. As shown. the collection electrodes and the various sub-passages extend through to station 5. and thereby the aspect ratio is not constant between stations 4 and length from that point to the outlet to theheight at that point.

. t.-n th Aspect Ratio Presuming an inlet height oi 24 inches. and a gas passage length of 32 inches. the aspect ratio at station I is 1.33. At station 2. where the height is lit inches and the length to the outlet 24 inches. the aspect ratio is l.33. The aspect ratio is L33 at station 3. where the height is l2 inches and the remaining length is l6 inches. At station 4. the height is 6 inches and the remaining length is 8 inches. Again. the aspect ratio is L33. The aspect ratio in the secondary section of the precipitator. between stations 4 and S. does not remain constant. The secondary section is provided so that attachment to gas exhaustductwork less than 6 inches in height can be made. However. it should be understood that the outlet of the precipitator could be at station 4.

FIG. 3 is a vertical longitudinal sectional view oftypical prior art prccipitator. Top 40 and bottom 42 are equidistant throughout the entire length of the device. Therefore. the aspect ratio will decrease markedly from inlet to outlet. The height is'24 inches. and the length is 32 inches. just as illustrated with regard to the inventive device. The aspect ratio at station i is l.33. At station 2. the aspect ratio drops to 1.0; at station 3 to 0.66. and at station 4 to 0.33. The comparison between the prior art devices. and the inventive device. V is showngraphically in FIG. 4.

The configuration oi top 18 and bottom 16 are shown in FIGS. IA and 2. The top and bottom diverge from inlet to outlet. The divergence ol'the top 18 and bottom l6. and the convergence of the sides Hand 14. are so related as to establish-a constant cross-sectional area throughout the length of the precipitator. in the examin the form of ver 5. However. these elements need not extend into that section of the precipitator.

The electrostatic chargeis imparted to the particles by a plurality of discharge electrodes in the form of wires 80. These extend down the center of the various passages. The number and placement of discharge electrodes and collection electrodes depends on a number of factors. but the general idea is to maximize the exposure of the particles.

Many variations and modifications of the embodiment illustrated are possible. and are within the contemplated realm of this invention. For example. the dimensional relationship may be varied from those illustrated. The supplementary section between stations 4 r and 5 can be omitted. Also. the precipitator could be operated in reverse flow. upon which the aspect ratio would not be constant. but would sharply decrease. providing special effects.

The invention is defined by the scope of the appended claims.

i claim: l. A gas fiow passage for an electrostatic precipitator comprising a bottom panel. atop panel.

a pair of opposed side panels joined to said top panel and said bottom panel to define a gas flow passage having an inlet and an outlet. the height of each of said side panels diminishing from said inlet to said outlet at such a rate as to maintain constant the aspect ratio. which is defined as the ratio between the distance from a point of measurement to the outlet along the length of the precipitator. and the height 7 *3. The apparatus ot claim 2 wherein the crosssectionul area. of said gas passage remains constant from said inlet tosald outlet.

4. The apparatus of claim 3 further comprising a scc- .ondary gas passage attached to said gas passage at the r outlet thereof. the cross-sectional area of said secondary gas passage being equal to the. cross-sectional area of said gas passage and constant throughout the length a of said secondary gas passage.

5. The apparatus of claim I lttrther comprising means by dividing said gas passage into a plurality of subpassages for at least a portion of the length thereof.

each of said sub-passages having a constant aspect ratio moved from collection electrodes by conventional methods. such as by interrupting or reversing the charging cu rrent. or by striking the collection electrode I throughout the length thereof.

6. The apparatus of claim 5 wherein said gas passage has a constant cross-sectional area between said inlet and said outlet. wherein each of said sub-passages has a constant cross-sectional area throughout the entire 7 length thereof.

7. An electrostatic precipitator comprising:

a gas passage defined by a top panel. a bottom panel.

' and a pair of opposed side panels attached to said top panel and said bottom panel and having an inlet and an outlet. said top panel and said bottom panel convergingifrom said inlet to said outlet such that the aspect ratio remains constant from said inlet to said outlet.

discharge electrode means positioned in said gas pasv sage. and collection electrode means positioned sage. I

8. The electrostatic precipitator of claim 7 wherein said side panels diverge from said inlet to said outlet. and wherein said collection electrode means comprises at least one collection electrode panel extending from said top panel to said bottom panel along at least a porin said gas pasis constant from said inlet to said outlet.

10. The electrostatic precipitator of claim 9 wherein said collection electrode means comprises at least one collection electrode panel extending from said top panel to said bottom panel along at least a portion of the length of said gas passage and dividing said gas passage into a plurality of sub passages. each of said subpassages having a constant aspect ratio for the entire length thereof.

i i i i 

1. A gas flow passage for an electrostatic precipitator comprising a bottom panel, a top panel, a pair of opposed side panels joined to said top panel and said bottom panel to define a gas flow passage having an inlet and an outlet, the height of each of said side panels diminishing from said inlet to said outlet at such a rate as to maintain constant the aspect ratio, which is defined as the ratio between the distance from a point of measurement to the outlet along the length of the precipitator, and the height at said point.
 2. The apparatus of claim 1 wherein the width of said gas flow passage increases from said inlet to said outlet.
 3. The apparatus of claim 2 wherein the cross-sectional area of said gas passage remains constant from said inlet to said outlet.
 4. The apparatus of claim 3 further comprising a secondary gas passage attached to said gas passage at the outlet thereof, the cross-sectional area of said secondary gas passage being equal to the cross-sectional area of said gas passage and constant throughout the length of said secondary gas passage.
 5. The apparatus of claim 1 further comprising means dividing said gas passage into a plurality of sub-passages for at least a portion of the length thereof, each of said sub-passages having a constant aspect ratio throughout the length thereof.
 6. The apparatus of claim 5 wherein said gas passage has a constant cross-sectional area between said inlet and said outlet, wherein each of said sub-passages has a constant cross-sectional area throughout the entire length thereof.
 7. AN ELECTROSTATIC PRECIPITATOR COMPRISING: A GAS PASSAGE DEFINED BY A TOP PANEL, A BOTTOM PANEL, AND A PAIR OF OPPOSED SIDE PANELS ATTACHED TO SAID TOP PANEL AND SAID BOTTOM PANEL AND HAVING AN INLET AND AN OUTLET, SAID TOP PANEL AND SAID BOTTOM PANEL CONVERGING FROM SAID INLET TO SAID OUTLET SUCH THAT THE ASPECT RATIO REMAINS CONSTANT FROM SAID INLET TO SAID OUTLET, DISCHARGE ELECTRODE MEANS POSITIONED IN SAID GAS PASSAGE, AND COLLECTION ELECTRODE MEANS POSITIONED IN SAID GAS PASSAGE.
 8. The electrostatic precipitator of claim 7 wherein said side panels diverge from said inlet to said outlet, and wherein said collection electrode means comprises at least one collection electrode panel extending from said top panel to said bottom panel along at least a portion of the length of said gas passage and dividing said gas passage into a plurality of sub-passages, each of said sub-passages having a constant aspect ratio for the entire length thereof.
 9. The electrostatic precipitator of claim 8 wherein said side panels diverge from said inlet to said outlet, and wherein the cross-sectional area of said gas passage is constant from said inlet to said outlet.
 10. The electrostatic precipitator of claim 9 wherein said collection electrode means comprises at least one collection electrode panel extending from said top panel to said bottom panel along at least a portion of the length of said gas passage and dividing said gas passage into a plurality of sub-passages, each of said sub-passages having a constant aspect ratio for the entire length thereof. 